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14mm Automatic Air Rifle

Built a pneumatic cannon? Then post it here! This section is for completed, finished cannons that you have built. Please include pictures and information.
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14mm Automatic Air Rifle

Unread postAuthor: al-xg » Wed Sep 23, 2009 5:57 pm

A few MS Paint drawings to illustrate inner workings of the Design #3 of the innovative contest...
http://www.spudfiles.com/forums/cannon-3-14mm-automatic-air-rifle-t19145.html
Image

Although the delayed blow-back seems to be the central feature of this airgun, it was just an easier and more efficient option compared to direct blowback.
I decided on using blowback, instead of blow forward, as I liked the idea that the new projectile is loaded after the shot not during.
Also air flow, using this setup, isn't as restricted.
I had originally planed on using a chamber connected air ram to operate the bolt, but the cocking action on a blowback system just seemed really satisfying :)
The delayed aspect was appealing as it uses pressure left over after the projectile is up to speed, and has positive effects on noise reduction and muzzle blast.
(Then again, a new problem showed up as far as sound levels were concerned. Overall sound levels were reduced to the extent that at short range projectile impact is much louder than the shot, but firing from the shoulder became uncomfortable. A problem often attributed to bullpup designs. Some will probably say, "shoot a real gun you'll fin out what loud is", but as far as I'm concerned if it makes your ears ring then its not good.)

So first of all, here is a cross section of the gas piston.
It a pretty basic component. I will operate even when dry firing, but the bolt then doesn't move back all the way.
The piston is made from 20mm aluminium tube and epoxy based paste.
The outer tube is 22mm copper. The air seal is achieved thanks to silicone lubricant and a large enough surface area.
Image The gas piston was built in such a way to be able to remove it or move it up or down the barrel. The closer to the muzzle the better, but if the bolt remains locked for too long it might not receive enough pressure to recoil

Here is an exploded view of the loading assembly:
Image

Parts of the QEV and fittings that were modified for more efficient flow (in red):
Image

Even though it was presented in the inovative design contest, this air rifle was originaly meant to be used for attemping some long range (in the world of big bore air rifles) target shots. (The idea was to produce some sort of scaled down gepard M6, firing the yet to come 14.5 Whisper round :wink:, only using compressed air.)
The original specs I wanted to achieve were along the lines of:

-muzzle velocity of at least 230m/s
-effective range of 200+m on a large target (not expecting extreme accuracy at that range)
-at least the possiblity of semi-automatic fire
-air efficient but using a QEV, so minimal pilot volume, good flow through valve, minimal losses through loading mechanism, maximum barrel length etc...
-A reasonable amount of shots without having to refill (enough to hopefully make a few succesful long range shots)
-portable and practical
-try for good consistency and accuracy
-give the possiblity of experimenting with the diesel effect
-be classed as a bigbore airgun

I then added:

-Automatic fire ability
-Select fire abilty (easy to do, without tools)
-A cool way of manualy cycling the action

And then decided the automatic fire should not be any less powerful than semi-automatic or single shot.

I had at first designed a fully pneumatic firing system, but the select fire wasn't as straight forward as a 3 position switch and automatic fire would have relied on a pop off set up, making full auto shots less powerfull.
Fully pneumatic select fire (using only one trigger) can be achieved using a manual 5/2 valve and two small ballvalves. The only action needed would be to use the ballvalves. Although one of them would have to be ajusted with care (a mark could be used) to an intermediate position as it controls the rate of fire the pop off valve generates.

The electronic 3 way valve set up, is more efficient during automatic fire, and prevents firing in the event of a jam during loading of a projectile(it saves suffering an explosion of high pressure air to the face).
Also it is much more compact and using a microswitch as a trigger is very convienient.

Some RLD (not quite Very Low Drag, bur Reasonably Low Drag :wink: ) bullets were designed. Even though at subsonic speeds the effect of aerodynamic drag isn't as great, the flight time to target is still noticably reduced. The bullets could have been streamlined some more, but then loss of velocity due to weight and high twist rates required for stabilisation become an issue when increasing the projectile length.

As you will have noticed, the build I made of the #3 contest entry was disapointing. I only started it once I realised it was going to be too late, and that happened to be while, amongst other time consuming activities, preparing to move to another country. I won't have the opportunity to work on any spudgun related projects in a while, so decided to post it anyway, as there was no avantage in keeping it for later.

I do have one video of the pump action, unlocking and moving the bolt back (which turned out to be out of focus), but just didn't have time to film any later features. I'll try and upload it.
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Last edited by al-xg on Thu Sep 24, 2009 5:46 pm, edited 1 time in total.
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Unread postAuthor: inonickname » Wed Sep 23, 2009 10:25 pm

I like this design.. A lot more now diagrams, planning etc. have shown the insight you put into it.

How far away from the barrel tip did you place the blowback mechanism, and how hard of a spring did you use? Was it completely reliable?

I like it more than I did before..
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Unread postAuthor: jackssmirkingrevenge » Wed Sep 23, 2009 11:09 pm

Shame you didn't have time to reach its full potential, but good effort nonetheless.

If you actually managed to get the gas piston to work then some videos are definitely in order ;)
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Unread postAuthor: POLAND_SPUD » Thu Sep 24, 2009 4:42 am

nice.... I knew it was someone from Europe :D

I like the layout of the gun.. I mean the fact that it loads ammo from behind.. definitely that makes it look more rifle-like (and allows to use a relatively long barrel)

you mentioned that you couldn't reach high pressures because the solenoid valve leaks. It leaks via the solenoid part of it, right ??
I more or less know what you are talking about as I experienced something similar myself (dissembling and assembling again works but sooner or later it will start to leak)
manual valves should work better

I'd really like to see a video of it... it's a shame that you didn't have enough time but maybe you just wanted to achieve too many things with it
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Unread postAuthor: psycix » Thu Sep 24, 2009 5:41 am

If you would have managed to take a vid of it in proper operation, you would've won the contest, despite its looks.
It is not pretty, but the mechanism is great, and this gun is surely built out of pure innovation. If it was for me, you are the contest winner.
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Unread postAuthor: Brian the brain » Thu Sep 24, 2009 5:53 am

Damn..another idea of mine built by someone else first!
I'm all out of "new" ideas now!

I never actually firgured it would work well though. :?

I'm very impressed!!!
Now all it needs is some cleaning up and it will be one of the top guns on this site!!
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Oh my friggin god stop being so awesome, that thing is pure kick ass. Most innovative and creative pneumatic that the files have ever come by!

Can't ask for a better compliment!!
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Unread postAuthor: al-xg » Thu Sep 24, 2009 7:53 am

I am no longer in the same country as my build, so sadly any new material will have to wait till some time in december :/

I used a spring from an ajustable desk lamp, but also an elastic band. with delayed blow back, as long as the spring strong enough to the load projectiles it will work. It can be very weak compared to direct blow back.
I can't remember exactly but I have the feeling the piston is 25cm down the barrel, leaving 85cm of non ported barrel.
The gas piston itself is very reliable, it will move back with a dry fire and even when blowing through the barrel(but obviously not with much force)
The bolt on the other hand won't move back far enough if pressure in the barrel isn't sufficient (especially when using 40mm long bullets).
The bolt lock opens nearly regarless of the gas piston position on the barrel, as at a given pressure in the barrel the extra surface area on the gas piston and the leverage on the bolt lock is enough to overcome the force acting on the bolt.
The problem I had was that the bolt lock was made from low grade aluminium and the bolt endend up bending it back until it could no longer open. I did cut out a steel replacement but never got to use it.


The spring pushing the ferrous solenoid core against the seat will only hold it to about 400psi, streching the spring works for a while, but it would need to be replaced or be heat treated to last longer.
The solenoid body also leaked at only 145psi, but the cast epoxy solution fixed that perfectly.


With this design semi auto is fine, but because of the bore size, high pressure is needed in order to fill the chamber fast enough. One could reduce the chamber volume instead, but I wanted decent muzzle velocity/energy.
One could add another microswitch, or a ready made pressure switch to the chamber to make sure the shot is fired only once the chamber is fully pressurised. But for a good ROF in that caliber high pressure is better.


I had plenty of time but started too late, mainly as I was hopping to use the custom valve I'd designed. The valve aswell as being a lot more efficient, has the reciever machined directly into it, so I shouldn't have had to make it out of that epoxy paste stuff. I was working in a precision aerospace engineering company at the time, so was planning on doing there, but the guy giving me acces to the machine tools (a 9 axis CNC lathe :D although 5 axis would have sufficed) got swine flu, then the workshop got really busy, then I had to go back to France, and well it still isn't finished. By the time I decided I'd have to use a regular QEV instead it was practicaly aready too late.

When I do get to work on it again, I will probably revert back to the chamber connected air ram loading but still using the solenoid valve and microswitches for semi and full auto select fire.
Using an air ram to move the bolt means it will work like a pressure switch for full auto, will cycle even with dry firing, projectile length will be less of an issue and it will also be able to run on lower pressures. (hopefully also less hurty for the ears)
The contest buil will probably be converted back to pump action just for fun.

I'll keep blowback for automatic fire with smaller calibers 6 or 8mm,as less air is needed for good power.

Oh and the actual chamber only extends as far as the grip, the rest of the tube was left there as a support.
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Unread postAuthor: Brian the brain » Thu Sep 24, 2009 11:46 am

I'd like to see how you made the bolt lock.
I understand it's function but I can't tell how you made it work..

When I thought up a similar system, I figured I'd use a large piston and a heavy spring unless I could think up a reliable boltlock.

I never built it, I'm sure I could have made some sort of bolt lock..but I'd like to see how you solved it
.I mean, does the bolt lock rod run over the lock or did you use a spring to keep it in place as the rest keeps going?

Also, my plan was to run a line from the muzzle to a piston near the bolt..
but I guess your idea is better as less air is needed to run it.A choice between volume and mass..

It would be easily built onto Old Shat..but I'd better build something new...a semi auto hammered qev gun could be made easy for everyone..
Your rifle inspires me to try my own version, maybe switch between semi and full auto....

I love your cannon and I think it sets a new standard!
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Oh my friggin god stop being so awesome, that thing is pure kick ass. Most innovative and creative pneumatic that the files have ever come by!

Can't ask for a better compliment!!
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Unread postAuthor: al-xg » Thu Sep 24, 2009 4:23 pm

I'm trying to upload that video, it shows the bolt lock opening.
I'm relying on a mobile internet connection though, hopefully it will work.

Ok, here we go...
[youtube]http://www.youtube.com/watch?v=qG6Nm_k05nY[/youtube]
The rod on the left hand side is is in contact with the gas piston and the grip.
The rod on the right hand side is connected to the front grip.
When the grip is pulled back the left hand rod makes contact first and pushes the bolt lock open, then the right hand rod pushes the bolt back.
The bolt lock clips back into place automatically thanks to an elastic band.
Due to its shape the bolt lock stops the bolt from moving back whilst firing. When the bolt rod pushes it open, it must move the bolt forward slightly before it releases it.

When the airgun is fired in semi-auto or automatic, the grip does't move and the bolt recoils using remaining pressure in the barrel.

When I fired the first test shots (with only one projectile in the mag), I thought the bolt wasn't being released, but it was just moving back to fast to see. I had to hold a pencil up to make sure the bolt was going back all the way and hitting it.

A BTB version of this design would be impressive :)
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Unread postAuthor: Pookydarts » Thu Sep 24, 2009 6:15 pm

psycix wrote:If you would have managed to take a vid of it in proper operation, you would've won the contest, despite its looks.
It is not pretty, but the mechanism is great, and this gun is surely built out of pure innovation. If it was for me, you are the contest winner.


I agree! I can't wait to see the second incarnation built with the high tech tools! :P Can I ask how you rifled the barrel and what sort of groups you're getting at whatever range you've worked at?

RLD projectiles made me laugh! I've spent sleepless nights worrying about the same things... :lol:

(Not really... but I do lay awake sometimes wondering how much trouble I'd get in if I got up 'just for five minutes' to run one more idea through GGDT :oops: :lol: )
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Unread postAuthor: jackssmirkingrevenge » Thu Sep 24, 2009 7:26 pm

Pookydarts wrote:RLD projectiles made me laugh! I've spent sleepless nights worrying about the same things... :lol:


We're not professional ballisticians after all, ELD projectiles are out of our league :roll:

(Not really... but I do lay awake sometimes wondering how much trouble I'd get in if I got up 'just for five minutes' to run one more idea through GGDT :oops: :lol: )


If past experience is anything to go by, truckloads! Damn it's good to be single :)
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Unread postAuthor: al-xg » Thu Sep 24, 2009 8:44 pm

The barrel is rifled using a homemade cutting tool.
http://www.spudfiles.com/forums/rifled-copper-barrel-t15685.html
I also have made some rifling tools by modifying old reamers, but they don't really give the possibility to experiment with different twist rates.
The rifling does stabilise oblong projectiles which is a start, and does provide tighter groupings than a smooth bore with oblong projectiles.
Accuracy seems alot more dependent on projectile and firing consistency.

I've shot 6 rounds into a 5cm circle at 15m, but that was just standing up and subject to my aiming abilities.
I haven't really tested long range accuracy, but I've hit large targets up to 200m away.
This was before I had a scope (just aiming down the barrel), so aiming at that range is more like pointing the barrel in the right general direction.

A grouping estimation at 200m would be a wild guess, but I do believe the flight of a stabilised lead projectile can be made fairly predictable using a homemade rifled barrel.

Sorry I can't be more accurate I just really not had enough time to try this out properly. To do so is one of the reasons I wanted to build this design.
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Unread postAuthor: Ragnarok » Thu Sep 24, 2009 8:55 pm

Personally, this is the idea that most impressed me from the contest.
I'm eagerly awaiting the opportunity of seeing it working as intended.

... and I'm not sure I can really say a huge amount more, partly because of the silly time of night. But...

jackssmirkingrevenge wrote:ELD projectiles are out of our league.

Speak for yourself. :twisted:
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Unread postAuthor: al-xg » Thu Sep 24, 2009 9:05 pm

Yes, I am actually wondering why on earth I'm still up posting...
(Not really... but I do lay awake sometimes wondering how much trouble I'd get in if I got up 'just for five minutes' to run one more idea through GGDT )

If past experience is anything to go by, truckloads! Damn it's good to be single

... and I'm not sure I can really say a huge amount more, partly because of the silly time of night. But...

:shock: must be infectious.

Well I'll sort that out... bedtime!
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Unread postAuthor: jackssmirkingrevenge » Thu Sep 24, 2009 10:40 pm

Bedtime schmedtime, I'm off to work :)

Ragnarok wrote:Speak for yourself. :twisted:


Let's see 'em then :D
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